Well, to me is not surprising actually.
If one wants to be good at swimming, dancing, playing baseball or anything, then it is important to start from the ground up and get better with practice, it is the same when comes to activities with need mental effort like learning a new language, writing and essay, translating a document or sorting out documents for people to find easily. With time and without further practice and effort our minds get numb and we get accustomed to a machine to do everything for us.
As it stands, the effects of long term AI use within working environments has not been studied yet, but I would not be anything beyond the scope of reality if more studies in the future showed the same negative results on individuals of all kind and working within all kinds of jobs where computers are required to enhance productivity.